Method for making ware by casting



Feb. 23, 1954 A. R. BLACKBURN ET AL METHOD FOR MAKING WARE BY CASTINGFiled Feb. 5, 1953 FIG. I.

3 Sheets-Sheet 1 INVENTOR ANDREW RLBLAOKBURN RICHARD E. STEELE M VJWATTORNEYS 1954 A. R. BLACKBURN ET AL I ,669,7

METHOD FOR MAKING WARE BY CASTING Filed Feb. 5, 1953 3 Sheets-Sheet 2INVENTOR ANDRE R. BLACKBURN RICH D E. STEELE ATTORNEYS 1954 A. R.BLACKBURN ET AL 2,669,762

METHOD FDR MAKING WARE BY CASTING Filed Feb. 5, 1955 5 Sheets-Sheet sINVENTOR NDREW R. BLACKBURN RiCHARD E. STEELE ATTORNEYS Patented Feb.23, 1954 UNITED STATES;

RATENT OFFICE Andrew R. Blackburn and Richard E. Steel Columbus, OhioApplication February 5, 1953, Serial No. 335,292

1 Claim. 1

stant application for patent.

In both solid casting methods as presently employed the formed object isseparated finally from the mold by the shrinkage action inherent in theobject upon losing a portion of its water of plasticity. However certainmold sections can be removed from contact with the ware before the wareshrinkage has progressed to any appreciable degree, in order to preventcontraction of the object about the mold section and without damagingthe easily deformed object as long as the object is sufficientlysupported by the remaining mold parts. istics and water retentiveproperties of the different slip or casting preparations varyconsiderably. This factor, in addition to the reconditioning periodrequired for a mold to free itself of its held water and thus restoreits absorption properties has prevented the rapid production of ceramicware from a one mold unit and it has been necessary to employ largenumbers of molds in an object forming operation in order to over come tosome extent the delay inherent in shrinkage release of objects frommolds.

It follows that multiple porous molds have been employed to acceleratewater absorption from a'slip. Shrinkage of the formed object thusbecomes a function of the porosity of the mold and the water retentioncapabilities of the cast object. While the production rate is thusaccelerated, the presence of the two variable factors effectingshrinkage contribute to a lack of uniformity in the end product.

This is especially the case with the molding of objects having differentthickness measurements in which the overall shrinkage rate is impossibleto anticipate, except by tedious experiment with different types ofcasting materials and repeated object casting until a perfect object isproduced. Generally, irregular shrinkage results me high percentage ofbreakage during and subsequent to removing the object from 1 the moldfaces, and shattering during the finish- The shrinkage character- 2, ingoperations from stresses developed in the ware structure. This isparticularly the case with ware having, for example, a thin base andthickened sides, or vice versa.

Solid casting regardless of whether the slip is forced into a cavity bygravity only or injected into a cavity by elevated pressures, above thatof the gravity feed is generally conducted at present along thefollowing lines. The slip or fluid casting preparation is introduced orinjected into an object forming cavity of the mold. The mold usuallyconsists of two or more sections and is made from one of the suitablegypsum plasters or other suitable mold material. The slip which may beprepared from a variety of ceramic raw materials, and well known to theart, is characterized by a higher specific gravity than that typerequired for ordinary draincasting and may in the case of pressurecasting have a livery consistency. In pressure feed casting there is noneed for the slip to flow freely.

After introduction of a slip, the charge must remain in contact with theentire object forming cavity of the mold until, by the process ofabsorption of the water from the slip by the mold or by forcing thewater into the mold as a result of extreme slip pressures, the chargewithin takes on the character of a solid throughout, at which time theformed charge commences to undergo normal shrinkage. If at this timethere is any tendency in the formed charge orfobject to contract andbind upon any of a plurality of mold sections, such as the core portionof a mold forming the interior of an object, such a section may beremoved manually, by exercising extreme care, from contact with theobject. Such mold sections have been withdrawn from the formed object bypressurizing, a section bymeans of a conduit extending into the moldsection. When such a type of mold section withdrawal is practiced, theobject is backed up by other supporting mold sections and the entiremold is in the closed position when pressurized.

Mold sections are also sometimes removed so that the exposed were withits supporting mold members may be subjected to a drying treatment tohasten the final shrinkage release of the formed object. Although it ispossible to remove special sections of the mold soon aftersolidification, the object for a time remains in an easily deformablecondition and adheres to the remaining mold members until finallyreleased by the shrinkage inherent in-the object.

The molds are usua1ly Worked in the proximity 3 of a drying means so asto keep the molds in a workable condition.

Dry molds are most imperative for gravity casting which depends largelyupon the absorption properties of the plaster and where at bestproduction may not exceed 6 pieces per mold per day, and may be nogreater than 1 piece per day. Although it is true that dry molds are notas necessary for pressure casting; -the waterw being forcedinto the moldunder pressurecarries small colloidal particles and other harmfulsoluble materials into the pores and soon blocks them'to further use.

The present invention has for an object the provision of a novel method'and' means' 'ror the manufacture of ceramic ware, wherein the abovementioned disadvantages are obviated.

A further object is to provide a novel method and apparatus for formingceramic objectswhich may be employed in combination with present:manufactnre'enethodsi to .increasesmarkedlyl the -rprodution rateadvantageous for rcembination -wu'th,.;-processes :-..The invention 1articularly which are unsuccessful due to. limitationinhandlinge certaintypes of mcldable materiaiss such erasare used-incasting, whichiwhenhandled often result 2 in unsatisfactory objecta'elease from the :mold,l. causing! the obj ect to warp er :crack.

:-.-Apfurther. obj ectdsnto provide novel; method sand; apparatus zfortthetnmanufacture refiners-mic ifurthelx object is to i providemethodna-nd a apparatus; for the manufacture of ceramic ware 'wWhGIGlILthrough :quiclc-releasetofsthe object from the ."mo1d,1ahigh speed;.prodnction rate attained; without:sacrificingsthe quality: of. product1 and withimarked reduction" of -..-unit; cost.

A fUI'thQFzGbjQCt'rlSitOlEI'OVidfi-Q; method and apparatus for forming"-twarewherein adherence of .the formed. object :to rthe .mold trace orfaces cant .be controlled by- :the.v operator, u'irrespective ,of.-.shrinkage characteristics or ldensitycof. .tlie

. molded object.

:A further: object .iswto;.provide-a:novel method wand aapparatusfor for-ming ware-of l. irregular shape or; thickness "whereinthe effect of.differen- ,tial shrmkage-on separation .ofla formed obiect .from the:rnold, iseliminated and. the number: of -;molds necessary for.accomplishing. arcont-in-uous 101318617 forming: operation-is minimized.

;. A.further. object .is. to-providea .novelimethod forleffectingthequick release of. ceramic objects from. -mold surfaces,- without.iniuring the .zware, before. normal. shrinkagei..occurs.

A further .objectis to provide.a nove1.m,ethod and apparatus. for themanufacture; of asymetri- "cally shaped clay objects. Still a furtherobjectistogprovide. a novel-mold *for use-in-castingceramic'objectswhich is .in'ex- -penSiVelyand' easilyfabricated;'permittingpf frequent designchanges;an'davliich-is'adapt'able for :use 'with presently employed"casting processes andzapparatus- .;:An :addition'al object resides in Ithe provision .;of :means: and cmethod :foryacuum removalof e-absorbed?fluids 'from mold tsectionsrssuch as are expressed. from tlrermolded objectt into ther'ni'old sectionsnand subsequently :purging memainingflu-ids. not previously *.evacuated from "the zmold sections.

nn additionaland related-iobgect-;resides.inthe iinitial reduction -.ofpressures within molds-secs 5 to the cleansing of the pores of the mold,following casting, a desired purging action eliminating sealing ofporous molding surfaces by adjacent colloidal particles, and otherharmful soluble impurities.

Anot'hcr object of the invention is to provide a means for increasingceramic mold life by the --continual reduction of saturation of a moldor moldsduringuse avoiding reliance upon expensive dr 'ing equipment.

1.;. Others'objects and advantages of the present invention will befound in the following detailed ..descr iption-.thereof and theaccompanying drawings, wherein:

'iFigure 1 is a vertical section of the mold of the present invention;with the male and female :mold sectionabrought "together .inwclampineneasement;

. Figureszsisea partial top-plan (view of;- the':.fecmalenmoldttakenalong the line 2-:-2.-of Eigureil;

Fg-igiure "3 is -.a-perspecti-veview -,of a mortiomof .cliuid pressure.conduiteemployed in :,forming .the

mold.

.Figure 4. is avertical :section ,ofathetinvention wherein multiplecasting: sections in-iexcessofa-two are employed;

Figure-5 is a partiaLtopplan-yiew oflthemodification. shownin r Figure.4 taken. alongr-the line 5-5 of Figure 4.

Initsv broadest application, ,the. :inventionscomprises (a.novel..me.thodand;.means of :separating -ceramic. objectsfrommoldsurfaces. by-theapplication of. fluid .pressure uniformly-against .the.faceof the formedobjectdesired torbe=separated ..controlling the.pressureiin .selected areasdrnac- .cordance with ..the. requirements.of .obi ect .thickinesstand ,shape. JIYhe. sourceof ,pressure.is,.-pr.ef-

.erably sodisposed.inurelation to..the contourand .anyselected.areanofsthe. object as-.to ..provide a predictable, controlled .force.in thefiform .of. a pressure blanket exerted simultaneously..across the.entire .surface.area..of.-the.cenamiclobject,iin

accordance with. a.pre:s'electedpressuretpattern, wherebyreleaseof.theobjectjrom themoldsurface is accomplished without.-imparting..-.nnclue shock or straintoltheobjectonany part thereof.

'The inventionmay be emialoyedsatiSfabtorily with .known forming,processessuch, as ...casti ng under varying conditions wherein.,thecaSting materials are tempered with water orOther mediums and whichnormally .employ shrinkage release of the object from v.the.mold..jSucn. old

processes are characterized .byextremely.;.slow rate of .production, dueto thainabilityto release the. ware :from .the .casting...m'olds.are...normal shrinkage 'which occurs ."by i the Telapsel .oft1time."However, the .invention 'is "most advantageously employed with"formin'gprocesses" wherein .uniform shrinkage r'elease-ofthe objectvfrom "the =mold is difiicult or impossible. The invention permits ofemploying mass production methods without a, great need'forimanyduplicate molds. An ordinary casting operation thatiformerly took:hours' for a singleobject now'for .the.;first..time can be accomplishedin minutes. ..J.Eor..instance,

" the. art of. pressure casting had practical1y,.be-

come obscure ..until thepresent invention. .lNow,

.however,.-longy. mold life, clear post-casting 1 mold zsurfacesaaremade readily available andzthere is .IaireviYal. .of-a valuable art.

,1 7s hea invention; may .be ;employed 'zwithu'gravity aeca'zea solidcasting, drain casting, and external pressure solid casting where theslip used is of a higher specific gravity than normally employed ingravity casting. For purposes of illustration, invention will bedescribed as employed in ex' ternal pressure and gravity pressurecasting, the 1 other methods and devices for carrying out relatedprocesses having been described in our United States Patent No.2,58%,109 entitled Method and Y Apparatus for Making Ware, issuedFebruary 5, j 1952. It will be readily apparent, however, that theprinciples of the invention may be applied equally well to other methodsof forming ceramic ware.

Referring to the drawings, the numeral It refers generally to a moldconstructed in accordance with the invention, including a top or femalemold section l2 and a bottom male mold section l4. Each mold section isformed in a casing l6,

:' which may be constructed of any corrosion resistant material such asalloy steel, which may be assembled by welding. In one form of theinvention the casings are perforated as at I8 to facilitate purging inthe manufacture of the mold body and to eliminate the development ofinterfering back pressures in the passage of fluid pressure through themold for the release of ware and cleansing of the molding face of themold body.

In another form of the invention, the casings I l 6 are sealed to retainpressure and liquid seepage during a casting operation.

The bodies l2 and I4 of the apparatus are formed of a material capableof hardening upon standing to form a solid porous and permeable elementcharacterized by an ability to absorb moisture. A high grade of gypsumplaster or other suitable hydraulic setting cements may be employed. Itis preferred to use a hard gypsum cement rather than soft plaster inview of itsiex- I treme hardness. longs the life of the mold. Theplaster body Such a cement markedly pro- I molding faces and 22 byimpression with suit- I able forms prior to hardening of the moldmaterial.

A. cavity 24 is formed by the opposed molding faces 20 and 22, thecavity beingsealed as at 26, where complementary surfaces of therespective mold. bodies engage.

Mold section 12 forms channel 28 which passes from the exterior of thecasing H3 inwardly to the molding face 22. This channel 28 employed tointroduce slip under pressure into cavity 24.

The channel walls 30 may be impregnated with suitable sealers to renderthem impervious to slip and to fluids. A conduit 32 is threaded into thecylindrical wall 30 of channel 28 providing valved passage forthe" slipfrom a pressurized reservoir 36. The flow control valve is designated asat 34. Slip maybe introduced to the reservoir through an inlet conduit38. The reservoir is pressurized by means not shown. l

Clamping means 42 are attached to the exterior of the casings It tosecure the mold'bodies-to- 5 gether. The clamping means maybe aconventiona'l butterfly nut-clamp arrangement. In accordance with thepresent invention, fluid pressure means are formed in the plaster bodiesl2 and I4 for effecting removal of a clay object 40 from either or bothof the mold faces 2|] and 22, preferably prior to shrinkage normallyoccurring upon losing a portion of water of plasticity of the clay. Saidmeans include a conduit 44 having an extension 46 passing through thecasing of the mold body to a source of fluid pressure, not shown. Theconduit 44 may preferably comprise a tubular member formed of an easilyworkable material which is corrosion resistant, such as a metal.

- The conduit 44 may be supported against radial displacement by one ormore bracket members opening into the body of the plaster molds.

45. The bracket 45 is formed to engage with any section of the conduitin order primarily to secure the conduit 44 firmly during formation andas the plaster mold hardens. The plaster casts l2 and I4 may be lockedin the mold by dimpling the casings I6 as at different portions thereof19, thereby preventing accidental displacement of the plaster casts inor from the molds upon the application of fluid pressures to the conduit44.

Referring to Figures 2 and 3, the conduit 44 is apertured as at 48 alongits length, the apertures The apertures 48 are formed to provide aplurality of streams of fluid pressure in such a manner to provide anevenly dispersed blanket of pressure across the face of the clay objectadjacent the mold surfaces 20 and 22. The conduit 44 is preshaped toprovide evenly spaced sources of fluid pressure about the entire face ofthe object 40. To accomplish this, the conduit 44 in one configuration,preferably is formed as a helix, with the coils thereof positionedinternally of a mold section away from the face of the mold section butgenerally parallel to the contour of the clay object 40. In someinstances, the conduit will be wound concentrically about itself asshown at the top of the mold body 12.

The spacing and size of the pressure apertures 48 and the distancebetween a section of the conduit 44 and the adjacent face of the clayobject 40 and the spacing between related portions of the conduitdestermine the amount of fluid pressure which will be exerted on aportion of the clay object. By adjusting these variables, a controlledadherence of the clay object to the mold surfaces is accomplished. Theoperator may obtain adherence of any portion of the ware to any desiredpart of the mold for a. preferred length of time, by exercise of thisavailable control of the were I releasing pressure. Thus, regardless ofthe relative or differential thicknesses of the several parts of theware, as for example the beaker shown in Figure 1, a fully controlledquick release of the object from the mold may be accomplished, withoutdanger of injury to the ware from the ever present tendency to crack atthe thin], points, upon the application of pressures thereto. It will beappreciated that full release is not attempted herein with such time asthe setting may have i been, eifected and until the clamps have beenloosened sufiiciently to allow free release action.

As shown in Figure 3, it is preferred to enclose the conduit 44 withwrapping of permeable fab- .ric material such as gauze 5! The gauzeserves to maintain the apertures 48 free from obstruction through. theaccumulation of particles of plaster, and provides a pressure chamberbetween I the plaster and the conduit 44. Such a. chamber facilitatesbuilding up of a fluid pressure head outside the conduit M in the bodyof the porous plaster mold in the direction of the mold face,

' accelerating the passage of the fluid pressure .aza cecma 'ct'hroughzthe -body. -of=. thermold. .a-FIlhe-rconduite :un'ayibe pluggedtocform: a-..-dead.*.end-.1'n ithe-mold 'Jibddfy. :QtherEformoficonduitszmaywbesemployed ...includingforaminous. tubing ofsuiiiciently rig-id- .-iityito be selfsupporting. I

' rhemmethod 0f. manufacture of ia ipreferred tmold body-andthestructure ithereof iisrmore-iully disclosed and. claimed rinourUnited States Pat- -e1-1t:.-No. -2-;584,i-1O entitled --MoldandMethodzof i :Manuf-acture i-ssuedi Februaryb, 1952. -:-It-is 'pointacd=out therein \that-aconduit-such as Mrmay also I abet-formed.advantageously .by casting witmwax or .-aelowzmeitingv point =meta1alloy. zincludingi a bismuth.;alloy,. removable by."subjecti ng.-.th'emold to---e1evatedtemperatures as-'soon.-asthe plaster lhardens.

.Aimo-diiication- :of the invention-iszshowrrinaFi llles'rll and 5 of.the drawings. .A.-moldwgenera1ly o'mdicated as-at iii: comprises. mold-1sections-6.2;. ...-a.nd- 6.6. .xcasing .53 which maybe oonstructedof.any-corrosion-resistant: .rnaterial. fIfh-e 'casingsemay; .be..;pe1'forated or not :depending upon .th ..-type of castingidesired.

erably disposed with molding .-face 12 01. rmlold .iisection -fili. Inthisparticular modification,..mold --section E6 engagesreceivingsurfaces of. moldvsec- =.tions-.62- and15 i, the Tmold .section-66 forming a imale molding-surface as atfhi. Themolding-surfaces10,--'l2and 14..together form a-cavityJB @suitable. for receiving..s1ipeither. undercpressure .or-.by-. g1'.a vity feed as shown.In.:the..drawings .sshowmv-themold Bil is compietely assembledforcasting the cavity IScontainingby way of. illus- .-.-tration, zalslip 1ill] which has -been .introduccdby gravity feed.

:In the modificationin Figures. 4 and5;;a-funnel ,portion 78. .leading'into. a. :channe1..B0. .has .been

formed in the mold sectionsfiZ-and 54 respectivesubstantially ashereinbeforeldescribed. .In the mold bodies Hand 64 respectivlelmtheconduit 7 passes ai'cuatelyback .and forth across'ltheseniicircularsection thereof, the conduit beingIspaiced fat' distances critical fromthe.mblding"face .lllbf "I'th'e.mo'1d body. As hasbeenprevioushlexplained, 31'fihe1proxiniity o'f'the conduitmembertoithe. mold-."inglface of the mold i dependent upon the pordsitydesired in the endmold product. and the *"d'esiredn'eleasepressures to beuniformlyobtainedat the mold face. that the conduit will be disposedmore'prox'imate "thewnold face at portions adjacentheavier portions'ofthe 'ware and mor distantat portions adjacentthinner portions oftheware. However, the conduit may be placed equidistant'from the moldingface or otherwise disposed to e'fiect uni- Iform release. :Mold section6 4 contains. a conduit .JBA'LsubstantialIy similar tothat....defined,.for..the zmoidbodyfil .In the-mold section .66l.the-.conduit M84 .is likewise strategically displaced---within-.the

. Eachwmold sectioneis;,-provided =with=ia- It may be apparent;mo-ld":seotion-rdistantifromathe 2mo1dmg -iac t1l thereof. =.;Inrthis-.instanceihowever,.itaisipreferred :iithat uthe conduitwmember :besecured .helically aboutvthesinterior oftthe \mold seotioniandlcriti--cally distant :adjacent the. molding surface J4. -.'Ihe ;;pressureapertures I are indicated. as tats.

'- .-l'.likewise the disposition 1 of-the .oonduit 'through szmoldbodies 6 2 and-=64 respectively isiindicatedias -at QO-inFigure'S.

:01:18 ior'more bracket members a 92 protrude k inwardly :from thecasing1B8aof-each ofsthe respec- -tivemo1d sectionsto;provide:supporttothetubing s-structure -within'-.the-.mold duringtthedformation thereof. In addition there are provided recesses 1: 94fstrategicallyiabout ithe .interior ofsthe casing 68. to-securethe.-mo1d.. against movementwithin 1 thecasing member.

operation, the,. --principle. of the vinvention :rmayedoe employedainthe manufacture .hf ware ...from .a variety of.-.casting..materials. Asseparation from-uthe...mo1d :is accomplished priornto.shrinkagereleasaof. the clayobject, rthe .unpre- ;dictableresults.obtaining.from-theadifferinghcontraction propertie of.differenttypesof claysare eliminated as aproductioniactor. Accordingly.-.the invention. maybe .used tospeed. up .alLknown casting-methods ofware manufao-ture, .Whichnor .=mally require an houronmoreior'adequateohiect shrinkage to. occur before -thenlay. lobje'ctseparatesfromthemold.

A preferred type of 'sliplusedina.pressuracastring operation isrnormallyiof .greatefldensityi-than athatcmployed :in gravity castings.Accordingly, iand-inkeeping with current practice hereunder,

-'.a .1ivery .slip. maywbenforced .under .pressure .throughthe conduitand .intoothe .cavityliormed ,-by the. opposed-..mo1ding Ffaces. hi theanold .sec- -tions. :Atthis .time,.-.the.mold sections. may; beevacuated .-by.-.means-..ofc the. conduits within to .render the -mold-sections. morev .absorptive".fthus .accelerating .the setting actiono'fi;the.slip,'lthe .aslip-being.underpositivepressure w'ithin'the .cav-

.iity. iormed by. the. respective...mold.ifaces. T he..slipremainsincontact with the .mold cavity until Lthencharge .within.assumes fthecharacter .or a

:solid throughout [at which-Ltime. .it. commences toundergo normalshrinkage.

l Nowaiterwehavecast aovareobject, weseek ,itoremoveimoldsections'irom.the were, in. DIED- aration for the finalrelease ofthe ware,'by.means .,-.of..passing..fiuid pressure throughat.least. "one of the .mold. -sections. therebvlleaving lthe .lformedware'upon another. supporting mold section. ".The -..o1iowing.-stepmustbe undertaken'to removelthe ,formed warelirom the waresupportingmoldsec- .tion. ..The. supporting moldnow Lhas fluidpres- 1 sure; ipassed .itherethrough .to .the .molding face ;thereof, against the.iormed Ware to release ,the wareifrom. the. supporting .mold.section.

It will .be. appreciated ..that. .-.the .foregoing.ppwerative-description maybe..employed..to..describe .itheeprocess as-,-app1iedto. gravity: casting. and

draincasting.

NAT study .of..the-structure. of .the invention...w.ill disclose that .a.vacuum..-may..be "created .in either .one .ot-thdmolding units .to theexclusion-of .the other. and that ffluidpressures may be ap'plidtoeither surfaceofa cast obj.ect,..dependent.upon .lthe... qualitiesthereof desired. Various adapta- "tions in structure and operationthough. not. spe- ..cifica l1y -described .herein may. vbe..made withoutdeparting-tram the spirit. of ..the invention.

Qlt will be observed .that ithepresent invention provides .novelimethodsandimeans .fonlforming :...clay..;objects. 'zRossible. specificmuses include-the manufacture of dinner ware, art ware includingsculpture, decorative tile, terra cotta, refractories, and electricalporcelains. The controlled adherence principle of the invention may beemployed to advantage with all ware forming processes, allowing releaseof the ware from the mold sections at any point in the manufacturingoperation subsequent to casting.

Other obvious adaptations of the invention will occur to one familiarwith the art. The invention eomprehends the substitution of equivalents,Where possible, and is to be limited only as defined in the appendedclaim.

This application is a continuation in part of copending Blackburn andSteele application Serial No. 265,766 filed January 10, 1952, which wascopending with Blackburn and Steele application Serial No. 737,544, nowPatent No. 2,584,110, and Blackburn and Steele application Serial No.737,174, now Patent No. 2,584,109.

We claim:

A method for casting green ceramic ware in a porous mold and forseparating the cast ware completely from the mold after the ware hasbecome self-sustaining and, independently of the shrinkage of the ware,to promptly free the mold for reuse, which comprises causing a slip tofill a ware-forming cavity defined by a plurality of permeable moldmembers, maintaining said slip in said cavity in contact with said moldmembers for a time sufiicient to render said slip selfsustaining andform an easily deformable green piece of ware, thereafter before saidpiece shrinks appreciably (a) passing a fluid under pressure through afirst of said mold parts to release said piece therefrom and (b)separating said first mold part from said piece to leave said piecesupported only by the remaining mold parts and (c) thereafter passing afluid under pressure through said remaining mold parts to separate theunsupported piece completely therefrom and free the mold for reuse inthe formation of additional pieces of Ware.

ANDREW R. BLACKBURN.

RICHARD E. STEELE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,541,869 Sprenger June 16, 1925 1,784,373 Miller Dec. 9, 19302,026,624 Flower Jan. 7, 1936 2,273,016 Bower Feb. 17, 1942 2,584,109Blackburn et al. Feb. 5, 1952 2,584,110 Blackburn et a1 Feb. 5, 1952

